1. Field of the Invention
The present invention relates to an image reading apparatus, such as an image scanner, used for reading out images printed or drawn on an image-carrying medium.
2. Description of the Related Art
A conventional image reading apparatus is disclosed in JP-A-11(1999)-215301 for example. This apparatus, as shown in FIG. 8 of the accompanying drawings of the present application, includes a housing 91 upon which a transparent plate 90 is mounted. The housing 91 is made by molding awhile synthetic resin material. Inside the housing 91 is formed a light passage 92 defined by first and second wall surfaces 92a, 92b. 
The conventional image reading apparatus also includes an insulating substrate upon which a plurality of light sources (light-emitting diodes) 93 are mounted. As shown in FIG. 8, light is emitted from the light sources 93 and may be reflected on the wall surfaces 92a, 92b. Thus, the light is led to the image reading section Se on the upper surface of the transparent plate 90. Below the image reading section Se, the housing 91 supports a lens array 94 for focusing the reflected light from the image reading section Se onto a plurality of light-receiving elements 95 mounted on the insulating substrate. In accordance with the amount of received light, each of the elements 95 outputs image reading signals.
As stated above, the housing 91 of the conventional apparatus is produced by molding resin. Specifically, referring to FIG. 9 of the accompanying drawings, use is made of two molding pieces, namely, an upper molding piece 96 and a lower molding piece 97. The upper molding piece 97 is provided with a downward (first) projection 96a, while the lower molding piece 97 is provided with an upward (second) projection 97a. As seen from the figure, the first and the second projections 96a, 97a cooperate to form the light passage 92 of the housing 91.
In this manner, however, it is impossible to cause the upper portion 92a of the first wall surface 92a to protrude to the right (see arrow N1) beyond the lower portion 92bxe2x80x2 of the second wall surface 92b. Thus, in the conventional apparatus, the uppermost width L1 of the light passage 92 is made unduly large. Consequently, as shown in FIG. 8 (see arrows n), part of the light emitted from the light sources 93 will go out of the light passage 92 without illuminating the image reading section Se.
This disadvantage can be overcome by using a light reflector 98, as shown in FIG. 10 of the accompanying drawings, which is prepared separately from the housing 91 (the light reflector 98 is also disclosed in above-mentioned JP-A-11-215301). The reflector 98 is provided with a light shielding portion 98a protruding to the right beyond the lower portion 92bxe2x80x2 of the second wall surface. Because of this structure, the light passage 92 has an uppermost width L2 smaller than the width L1 of FIG. 8.
While having such an advantage, the second conventional apparatus of FIG. 10 has the following shortcomings. First, the preparation of the reflector 98, which needs to be produced separately from the housing 91, may impair the production efficiency and increase the production cost. Second, additional positioning means is required for holding the reflector 98 in place within the housing 91.
Further, the conventional apparatus of FIG. 10 (and the apparatus of FIG. 8 as well) is disadvantageous in the following respects. Specifically, in the apparatus of FIG. 10, the plurality of light sources 93 are spaced from each other in the longitudinal direction of the housing 91. Part of the light emitted from each light source 93 indirectly reaches the image reading section Se after being reflected (scattered, to be precise) by the wall surfaces defining the light passage 92, whereas the other part of the light directly reaches the section Se, traveling straight from the light source 93 to the section Se, as shown by the arrow n1 in FIG. 10. The indirect light from the light source 93 can uniformly illuminate the image reading section Se, since the indirect light, scattered by the wall surfaces, will be distributed uniformly over the length of the section Se. On the other hand, the direct light from the light sources 93 is not subjected to such scattering. Thus, as shown in FIG. 11, the direct light is liable to produce a non-uniform illuminating condition in which relatively bright portions BP and relatively dark portions DP are disposed alternately along the section Se. Clearly, such non-uniformity in brightness makes it difficult or even impossible to achieve accurate image reading operation.
Still further, in the conventional apparatus of FIG. 10 (and the one of FIG. 8), the lens array 94 is simply fitted into a lens holding groove formed in the housing 91. Thus, the lens array 94 may be displaced in the groove or even come out of the groove. Also, the lens array 94 may be thermally warped in the vertical direction.
The present invention has been proposed under the circumstances described above, and its object is to overcome the problems encountered in the conventional image reading apparatus.
According to the present invention, there is provided an image reading apparatus includes a housing provided with a light passage, a transparent plate mounted on the housing, a light source for emitting light into the light passage, a lens array facing an image reading section on the transparent plate, a plurality of light-receiving elements arranged in an array extending in a primary scanning direction, and a light reflector formed on the transparent plate. The reflector is offset from the image reading section in a secondary scanning direction perpendicular to the primary scanning direction.
The light reflector may be a white material applied on the transparent plate or a white strip member fixed to the transparent plate.
According to a preferred embodiment of the present invention, the light reflector may cover the entire surface of the transparent plate except a predetermined region facing the lens array.
Preferably, the apparatus of the present invention may further include a light blocker for preventing light from traveling directly from the light source to the image reading section.
Preferably, the housing may be provided with a plurality of inner wall surfaces defining the light passage, wherein the light blocker may be located on a particular one of the inner wall surfaces.
In a preferred embodiment of the present invention, the light source may be offset from the image reading section in the secondary scanning direction. In this case, the particular one of the inner wall surfaces may be located between the light source and the image reading section, as viewed in the secondary scanning direction.
Preferably, the light blocker may reflect light instead of absorbing light.
Preferably, the light blocker may be formed integral with the housing.
Preferably, the housing may be formed with a lens array fixing slit and an adhesive supplying bore communicating with the slit. Adhesive supplied in the adhesive supplying bore serves to hold the lens array in place.
Preferably, the apparatus of the present invention may further include a light absorber arranged to enclose the light-receiving elements. The light absorber may be provided with a contact portion held in engagement with the lens array, wherein the contact portion corresponds in position to the adhesive supplying bore.
Preferably, the adhesive supplying bore may be unopened toward the image reading section. With such an arrangement, a light-reflecting surface can be provided near the image reading section, whereby light is effectively directed toward the image reading section.
According to a preferred embodiment of the present invention, the adhesive supplying bore may be open in a direction going from the image reading section to the light-receiving elements.
Preferably, the housing may be formed with a lens array engaging member coming into engagement with a light-incident end of the lens array. In this manner, the lens array is reliably held in place or prevented from being thermally warped. In this case, the light absorber maybe provided with a contact portion held in engagement with the lens array, wherein the contact portion corresponds in position to the lens array engaging member.
Preferably, the light absorber may be dark-colored, in particular, black.
Preferably, the lens array may include an elongated holder and a plurality of lenses held together by the holder, wherein the contact portion of the light absorber may be held in engagement with the holder.
Preferably, the contact portion of the light absorber may be provided with a first contact surface and a second contact surface perpendicular to the first contact surface, wherein the lens array is supported by the first and the second contact surfaces.
Preferably, the contact portion of the light absorber may serve to prevent noise-causing light from reaching the light-receiving elements.